Lloyds TSB and Halifax, owned by Lloyds Banking Group, managed to re-establish normal services after an hour, and problems were fixed within two hours at the Co-op and Smile.

Many customers transferred to the Co-op following disruption to services at RBS and NatWest.

Industry experts were unable to explain why systems failures affected two separate banking groups at the same time on the same day.

Lloyds TSB customers took to Twitter to complain about the disruption. @SaladUK wrote: "My card was declined just now, it said 'Card declined' on the ATM but my internet banking is working. What's going on?."

@Emily_92 added: "Thanks a lot Lloyds TSB! It's not like I wanted to buy that shopping anyway. I just queued up for the fun of it!"

Co-op customer Jane Morley (@jm3twink) also weighed in: "Just had a panic as couldn't draw cash out but phoned bank & all Smile systems are down."

A Lloyds Banking Group spokesman said: "We experienced technical issues that affected some customers. All of our systems are now up and running. We are working hard to process the transactions impacted by this problem and they will be resolved before the close of play today.

"We know our customers rely on us, and we apologise for the inconvenience we have caused them."

A Co-op bank spokesperson said: "Our systems are fixed and customers should now be able to use their accounts as normal. We would like to apologise to those affected for the inconvenience caused by this temporary issue."

Customers of RBS and NatWest had their ordinary banking services back up and running within days, but the chaos affected Ulster Bank customers for a month.